The present invention relates in general to the manufacture of insulated concrete planks for use in walls and floors of building structures.
Reinforced precast, prestressed concrete planks or panels have been used for a number of years as wall and floor structures in buldings. Because of the increasing emphasis on producing well-insulated buildings, it became apparent some time ago that such planks were extremely poor in their insulation qualities. One approach to overcoming this defect of such panels was to cast panels in a "sandwich" configuration with a sheet of insulating material such as polyurethane or polystyrene between adjacent layers of concrete. Such a sandwich construction provided a noticeable improvement in the insulating qualities of the panel.
One of the problems which has been noted in sandwich concrete panels is the tendency of the top concrete layer to form stress cracks in the surface. It has been noted that such stress cracks most commonly form above the butt joint between adjacent pieces of insulating material. Such stress cracks have a highly undesirable cosmetic effect since the outer face layer of concrete is often exposed to view without any additional surface treatment being applied thereto.